1. Field of the Invention
The present invention relates generally to a method of estimating both the speed of an induction motor and the magnetic flux of a rotor, and more particularly to a method of estimating the speed of an induction motor and the magnetic flux of a rotor by use of parameters derived from some measurable or calculable variables.
2. Description of the Prior Art
In general, a speed control system for induction motors employs a system which feeds back the speed of the induction motor detected by a speed sensor installed in the motor, compares it with a speed command of the induction motor, and controls the speed of the induction motor according to an error resulted from the comparison.
However, as the speed sensor installed in the motor is susceptible of noise and has an installation limit, a variety of methods of estimating the speed of such motors without the speed sensor have been studied and developed, with one of them illustrated in FIG. 1.
FIG. 1 shows a schematic configuration of a conventional system for estimating the speed of an induction motor and the magnetic flux of a rotor. Referring to FIG. 1, the system 10 for estimating the speed of an induction motor and the magnetic flux of a rotor includes a full-order observer 11 for obtaining estimated values of current and magnetic flux, and a speed estimator 12 for estimating the speed of the induction motor by use of an actual current and the estimated values of current. Herein, the full-order observer 11 and the speed estimator 12 are not a mechanical device of general concept consisting of elements such as actual electrical parts or circuit components, but elements of a virtual device represented in a mechanical manner by an algorithm present in a program of a microprocessor.
The conventional system for estimating the speed of the induction motor and the magnetic flux of the rotor using such a sensorless vector control system measures a voltage vector Vds and a current vector ids of a voltage applied upon driving the induction motor, and obtains an estimated value of current and an estimated value of magnetic flux by use of the full-order observer 11. In addition, the speed of the induction motor is estimated by the speed estimator 12 by use of an error resulted from a comparison of the actual current with the estimated value of current.
However, as the conventional system for estimating the speed of the induction motor and the magnetic flux of the rotor requires a calculating equation for each of the current estimation, the magnetic flux estimation and the speed estimation, an amount of calculation is undesirably increased and an estimation algorithm must be performed during each performance period. This leads to a limitation in response characteristics of the motor speed control, resulting in deterioration of the system performance.
Accordingly, the present invention has been made keeping in mind the above problem occurring in the prior art, and an object of the present invention is to provide a method of estimating the speed of an induction motor and the magnetic flux of a rotor by use of parameters derived from some measurable or calculable variables, while reducing an amount of calculation.
In order to accomplish the above object, the present invention provides a method of estimating the speed of an induction motor and the magnetic flux of a rotor, comprising the steps of: a) obtaining some measurable or calculable variables for estimating the speed of the induction motor and the magnetic flux of the rotor; b) calculating a parameter as a counter-electromotive force of the motor derived from the variables obtained in the step a); c) estimating the speed of the motor by use of the parameter calculated in the step b), an estimated value of the parameter, and the obtained variables; and d) estimating the magnetic flux of the rotor by use of an estimated value of the speed estimated in the step c) and the parameter.